The present invention relates to a method for operation of a communication path between at least two communication terminals in which, at least at a start time, the two communication terminals are connected via at least one intermediate station and interchange signals with one another via this communication path, with both the intermediate station and the communication terminals determining the quality of signal transmission from the direction of their respective predecessor station or stations.
In multihop networks (multiple node networks), such as those which are being planned for the fourth generation of mobile radio networks, in addition to connections between one terminal and one base station, as used exclusively in the third mobile radio generation, connections are also possible which pass via two or more appliances, for example including other terminals, before they reach a base station or another terminal. The critical point with multihop networks is that the individual base stations, which are also referred to in the following text as hops (intermediate nodes) are connected to one another via the same air interface via which the end nodes also operate. This is the difference in comparison to conventional mobile radio networks in which the intermediate nodes are connected via cable networks or permanently installed directional radio paths.
If, by way of example, the nodes which are involved in a connection are moving, such as a node with a switching function in a vehicle, a situation may arise in which some of the intermediate nodes are unnecessary and can be removed from the connection. This may be expressed, for example, by two terminals which are alongside one another in the end effect, no longer being connected via the base station, as is normal nowadays, but communicating directly with one another.
Direct communication between two DECT connection terminals without having to communicate via a base station is already possible in the DECT (Digital European Cordless Telephone) field, that is to say for cordless telephony. However, this direct connection is not set up automatically, but manually.
One problem that arises in the optimization of a communication path between two communication terminals is to identify the capability to set up a new direct connection between the terminals, or a connection between the terminals via a better route length.
Laid-Open Specification US 2002086676 A1 has already described a method which initiates direct connections based on the knowledge of the geographical position of individual terminals. In order to allow this method to be implemented, the network, effectively as a central instance, has to know the position of the individual terminals and monitor these positions and, when necessary, has to send a request to the individual terminals to initiate a direct connection.
Furthermore, ad-hoc routing protocols exist, such as AODV (ad hoc On Demand Distance Vector routing) which use the entries in the routing tables to determine the maximum validity period for the existence of an intermediate node, after which the next intermediate node must be looked for once again. The end of this validity period, which is also referred to as a timeout, if appropriate, then leads to the initiation of new direct connections or to the confirmation of the existing next hop as the intermediate node.
The disadvantage of spatial localization of the individual terminals via the network is that the network, as the central monitoring unit, can be implemented only with a relatively high degree of hardware complexity. As such, the overall network configuration is very complex and inflexible.
Methods in which the maximum validity period for the existence of an intermediate node is determined via entries in routing tables, after which the next intermediate node must be looked for once again, have been found to have particularly high inertia. As a consequence, the power consumption during a switching action is unnecessarily high. Furthermore, the path search packets, which are transmitted cyclically like a flood wave, with this transmission generally being referred to as “flooding,” result in an unnecessarily high network load.
The present invention is therefore directed toward a method for operation of a communication path between at least two communication terminals which allows a connection between communication terminals via a better route length to be set up automatically, more quickly and more effectively, than with the previously known methods, or else which allows direct connections between communication terminals.